1. Field of the Invention
This invention relates to a slide fastener, and more particularly to a fastener stringer having a continuous plastic filament spirally formed and woven into an edge of a stringer tape during the weaving thereof by a needle loom.
2. Prior Art
There have been proposed a number of slide fasteners or zippers of the type described, which comprise a woven stringer tape and a plastic filament woven into a longitudinal edge of the tape, the filament being usually formed into a helical coil structure consisting of a row of successive elongated loops or convolutions each having a coupling head, an upper and a lower leg and a connecting portion.
Most of the known fasteners, however, have failed to meet with the requirements for the success of the so-called woven slide fasteners which largely depends upon the positional stability of the filament, i.e. coupling fastener element, with respect to the stringer tape against external stresses. When subjected to severe bending stresses in the transverse direction, the alignment or loop-to-loop pitch in the row of successive loops tends to be disturbed and the warp threads in particular holding the filament onto the tape are apt to shift out of place either toward the coupling head or toward the connecting or heel portion, which would in turn obstruct the movement of the slider and make it difficult to couple and uncouple the cooperating stringers.